Epidemiological studies on the effect of hepatitis in institutionalized mentally retarded patients have been continued. Patients with Down's Syndrome (DS) were matched with other mentally retarded (OMR) patients as to age, sex, resident ward, age at first institutionalization and length of institutionalization. Our data indicates that over the past 5 years the death rate in DS patients was approximately twice that of the OMR patients. The death rate among patients with chronic hepatitis B antigenemia is about twice that of patients without hepatitis B antigenemia. The death rate of DS patients with hepatitis B antigenemia is 4 times that of all other patients. Studies on the etiology of hepatitis A in institutionalized patients have been continued. Typical hepatitis A particles have been visualized in 4 of 12 fecal sample studies. Serological testing of serum for hepatitis A antibody in these patients is being undertaken. Studies on the association of hepatitis in pregnant women and observable disease in the newborn has been continued. Preliminary studies indicate that the etiology of Down's Syndrome is not associated with hepatitis A.